U.S. patent application number 11/611765 was filed with the patent office on 2007-06-21 for device and method for controlling output of rechargeable battery.
This patent application is currently assigned to PANASONIC EV ENERGY CO., LTD.. Invention is credited to Takuma Iida, Kouta Togashi.
Application Number | 20070138998 11/611765 |
Document ID | / |
Family ID | 38172672 |
Filed Date | 2007-06-21 |
United States Patent
Application |
20070138998 |
Kind Code |
A1 |
Togashi; Kouta ; et
al. |
June 21, 2007 |
DEVICE AND METHOD FOR CONTROLLING OUTPUT OF RECHARGEABLE
BATTERY
Abstract
A controller and method for controlling output of a rechargeable
battery that prevents the life span of the rechargeable battery
from being shortened while ensuring starting of the engine. The
rechargeable battery controller is mounted on a vehicle including
an engine functioning as a power source. The controller includes a
control unit for instructing a vehicle ECU, which is installed in
the vehicle, to stop discharging the rechargeable battery when an
index indicating the charged state of the rechargeable battery
satisfies a discharge suspension condition. The control unit
includes a monitor unit for changing the discharge suspension
condition so as to continue discharging the rechargeable battery
continues when the rechargeable battery is expected to supply power
to the starter motor of the engine.
Inventors: |
Togashi; Kouta; (Shizuoka,
JP) ; Iida; Takuma; (Shizuoka, JP) |
Correspondence
Address: |
WORKMAN NYDEGGER;(F/K/A WORKMAN NYDEGGER & SEELEY)
60 EAST SOUTH TEMPLE
1000 EAGLE GATE TOWER
SALT LAKE CITY
UT
84111
US
|
Assignee: |
PANASONIC EV ENERGY CO.,
LTD.
555, Sakaijuku, Kosai-shi
Shizuoka
JP
431-0452
|
Family ID: |
38172672 |
Appl. No.: |
11/611765 |
Filed: |
December 15, 2006 |
Current U.S.
Class: |
320/104 |
Current CPC
Class: |
B60L 2240/547 20130101;
Y02T 10/7072 20130101; B60L 2240/545 20130101; B60L 2240/662
20130101; Y02T 10/70 20130101; B60L 2270/20 20130101; H02J 1/14
20130101; B60L 58/13 20190201; B60L 2210/40 20130101; B60L 50/61
20190201; B60R 16/03 20130101; Y02T 10/92 20130101; B60L 3/0046
20130101; B60L 58/25 20190201; Y02T 10/72 20130101; Y02T 90/16
20130101; Y02T 10/62 20130101; B60L 50/16 20190201; H02J 2310/46
20200101 |
Class at
Publication: |
320/104 |
International
Class: |
H02J 7/00 20060101
H02J007/00 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 16, 2005 |
JP |
2005-363639 |
Claims
1. A controller for a rechargeable battery mounted on a vehicle
using an engine as a power source, the vehicle including a starter
motor for starting the engine and a vehicle controller for
controlling the starter motor, the controller comprising: a control
unit that when operated instructs the vehicle controller to stop
discharging the rechargeable battery when an index indicating a
charged state of the rechargeable battery satisfies a discharge
suspension condition, and moderates the discharge suspension
condition when the rechargeable battery is expected to supply power
to the starter motor.
2. The controller according to claim 1, wherein: the index
indicating the charged state of the rechargeable battery includes
terminal voltage of the rechargeable battery; the discharge
suspension condition includes a lower limit value for the terminal
voltage of the rechargeable battery; and the control unit lowers
the lower limit value of the terminal voltage to moderate the
discharge suspension condition.
3. The controller according to claim 1, wherein: the index
indicating the charged state of the rechargeable battery includes a
state of charge of the rechargeable battery; the discharge
suspension condition includes a lower limit value for the state of
charge of the rechargeable battery; and the control unit lowers the
lower limit value of the state of charge to moderate the discharge
suspension condition.
4. The controller according to claim 1, wherein: the index
indicating the charged state of the rechargeable battery includes
terminal voltage and state of charge of the rechargeable battery;
the discharge suspension condition includes lower limit values for
the terminal voltage and state of charge of the rechargeable
battery; and the control unit lowers the lower limit values of the
terminal voltage and state of charge of the rechargeable battery to
moderate the discharge suspension condition.
5. The controller according to claim 1, wherein: the rechargeable
battery has a temperature; and the control unit moderates the
discharge suspension condition if the temperature of the
rechargeable battery is lower than or equal to a predetermined
temperature when the rechargeable battery is expected to supply
power to the starter motor.
6. The controller according to claim 1, wherein the control unit
includes a monitor unit for changing the discharge suspension
condition so as to continue discharging the rechargeable battery
when the rechargeable battery is expected to supply power to the
starter motor.
7. The controller according to claim 1, wherein: the control unit
includes a setting unit for setting a first upper limit value and a
second upper limit value, which is lower than the first upper limit
value, for power discharged from the rechargeable battery within a
predetermined time; the discharge suspension condition includes a
first condition for generating an instruction based on the first
upper limit value to stop discharging the rechargeable battery and
a second condition for generating an instruction based on the
second upper limit value to stop discharging the rechargeable
battery; and the control unit moderates at least the first
condition.
8. The controller according to claim 7, wherein the first upper
limit value is set to be higher than the power required to be
discharged when starting the engine.
9. The controller according to claim 7, wherein the control unit
moderates the first condition during a period in which an engine
start signal provided from the vehicle controller to the
rechargeable battery controller is active.
10. A method for controlling output of a rechargeable battery
mounted on a vehicle using an engine as a power source, the vehicle
including a starter motor for starting the engine and a vehicle
controller for controlling the starter motor, the method
comprising: determining whether an index indicating a charged state
of the rechargeable battery satisfies a discharge suspension
condition; instructing the vehicle controller to stop discharging
the rechargeable battery when the index indicating the charged
state of the rechargeable battery satisfies the discharge
suspension condition; determining whether the rechargeable battery
is expected to supply power to the starter motor; and moderating
the discharge suspension condition when the rechargeable battery is
expected to supply power to the starter motor.
11. The method according to claim 10, wherein: the index indicating
the charged state of the rechargeable battery includes terminal
voltage of the rechargeable battery; the discharge suspension
condition includes a lower limit value for the terminal voltage of
the rechargeable battery; and said moderating the discharge
suspension condition includes lowering the lower limit value of the
terminal voltage.
12. The method according to claim 10, wherein: the index indicating
the charged state of the rechargeable battery includes a state of
charge of the rechargeable battery; the discharge suspension
condition includes a lower limit value for the state of charge of
the rechargeable battery; and said moderating the discharge
suspension condition includes lowering the lower limit value of the
state of charge.
13. The method according to claim 10, wherein: the index indicating
the charged state of the rechargeable battery includes terminal
voltage and state of charge of the rechargeable battery; the
discharge suspension condition includes lower limit values for the
terminal voltage and state of charge of the rechargeable battery;
and said moderating the discharge suspension condition includes
lowering the lower limit values of the terminal voltage and state
of charge of the rechargeable battery.
14. The method according to claim 10, wherein: the rechargeable
battery has a temperature; and said moderating the discharge
suspension condition includes moderating the discharge suspension
condition if the temperature of the rechargeable battery is lower
than or equal to a predetermined temperature when the rechargeable
battery is expected to supply power to the starter motor.
15. A computer-readable product encoded with program instructions
for execution by a computer for controlling output of a
rechargeable battery mounted on a vehicle using an engine as a
power source, the vehicle including a starter motor for starting
the engine and a vehicle controller for controlling the starter
motor, the program instructions when executed performing steps
comprising: determining whether an index indicating a charged state
of the rechargeable battery satisfies a discharge suspension
condition; instructing the vehicle controller to stop discharging
the rechargeable battery when the index indicating the charged
state of the rechargeable battery satisfies the discharge
suspension condition; determining whether the rechargeable battery
is expected to supply power to the starter motor; and moderating
the discharge suspension condition when the rechargeable battery is
expected to supply power to the starter motor.
16. The computer-readable product according to claim 15, wherein:
the index indicating the charged state of the rechargeable battery
includes terminal voltage of the rechargeable battery; the
discharge suspension condition includes a lower limit value for the
terminal voltage of the rechargeable battery; and said moderating
the discharge suspension condition includes lowering the lower
limit value of the terminal voltage.
17. The computer-readable product according to claim 15, wherein:
the index indicating the charged state of the rechargeable battery
includes a state of charge of the rechargeable battery; the
discharge suspension condition includes a lower limit value for the
state of charge of the rechargeable battery; and said moderating
the discharge suspension condition includes lowering the lower
limit value of the state of charge.
18. The computer-readable product according to claim 15, wherein:
the index indicating the charged state of the rechargeable battery
includes terminal voltage and state of charge of the rechargeable
battery; the discharge suspension condition includes lower limit
values for the terminal voltage and state of charge of the
rechargeable battery; and said moderating the discharge suspension
condition includes lowering the lower limit values of the terminal
voltage and state of charge of the rechargeable battery.
19. The computer-readable product according to claim 15, wherein:
the rechargeable battery has a temperature; and said moderating the
discharge suspension condition includes moderating the discharge
suspension condition if the temperature of the rechargeable battery
is lower than or equal to a predetermined temperature when the
rechargeable battery is expected to supply power to the starter
motor.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is based upon and claims the benefit of
priority from the prior Japanese Patent Application No.
2005-363639, filed on Dec. 16, 2005, the entire contents of which
are incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] The present invention relates to a device and a method for
controlling the output of a rechargeable battery mounted on a
vehicle.
[0003] A hybrid electric vehicle (HEV) using an engine and a motor
as a power source has been put to practical use and is becoming
popular. An HEV includes a rechargeable battery functioning as a
power supply for supplying power to the motor.
[0004] When the engine outputs more power than necessary to drive
the vehicle, the HEV drives its generator using the excessive power
to charge the rechargeable battery. When the vehicle is braking or
decelerating, the HEV drives the motor with the vehicle wheels and
charges the rechargeable battery using the motor as a power
generator. When the engine outputs less power than necessary, the
HEV compensates for the lack of power by discharging the
rechargeable battery and driving the motor.
[0005] In this way, the HEV accumulates energy in the rechargeable
battery. Conventional automobiles release such energy into the
atmosphere as heat. The energy efficiency of an HEV is higher than
the energy efficiency of a conventional automobile. Thus, the HEV
greatly improves fuel efficiency as compared with conventional
automobiles.
[0006] An HEV supplies power to a starter motor, which is used to
start the engine, with the rechargeable battery that supplies power
to the drive motor. However, in the rechargeable battery, the
discharge voltage or state of charge (SOC) greatly decreases at low
temperatures of zero degrees Celsius or lower. The HEV may not be
able to start the engine under such circumstances. Japanese
Laid-Open Patent Publication No. 2002-195138 describes a controller
(hereinafter referred to as "battery ECU") for a rechargeable
battery that limits the output of the discharged power to ensure
starting of the engine under low temperatures.
[0007] Specifically, the battery ECU sets the minimum voltage of
the rechargeable battery for driving the starter motor. If the
discharge voltage that was greater than or equal to the minimum
voltage when activating the starter motor becomes lowers than the
minimum voltage, the battery ECU temporarily stops the supply of
power. As discharge current generates heat in the battery and
increases the discharge voltage, the battery ECU allows power to be
supplied again to the starter motor. The battery ECU performs such
a process before the engine starts. Therefore, in the above
publication, the battery ECU ensures the starting of the engine
under low temperatures by repeatedly stopping and starting
discharge of the rechargeable battery.
[0008] The rechargeable battery mounted on the HEV is normally
formed by connecting a plurality battery cells in series. If the
capacity of each battery cell varies, the discharge capability of
each battery cell also varies. As a result, excess discharge of a
battery cell having a lowered capacity causes polarity inversion.
Repeated starting and stopping of discharge within a short period
of time also results in a tendency for polarity inversion to occur.
Thus, in the invention of the above publication that repeatedly
activates and inactivates the starter motor, the possibility of
rise in the frequency of polarity inversion increases. This
shortens the life span of the rechargeable battery.
SUMMARY OF THE INVENTION
[0009] The present invention provides a controller for the
rechargeable battery and method for controlling the rechargeable
battery that suppresses shortening of the life time of the
rechargeable battery while ensuring ability for the starting of the
engine.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] The invention, together with objects and advantages thereof,
may best be understood by reference to the following description of
the presently preferred embodiments together with the accompanying
drawings in which:
[0011] FIG. 1 is a schematic block diagram showing an electrical
configuration of a vehicle including a controller for the
rechargeable battery (battery ECU) according to a first embodiment
of the present invention;
[0012] FIG. 2 is a schematic block diagram of the battery ECU of
FIG. 1;
[0013] FIG. 3 is a graph showing changes in terminal voltage of the
rechargeable battery when an upper limit lowering process is
performed by a monitoring section of FIG. 2;
[0014] FIG. 4 is a graph showing the change in the terminal voltage
of the rechargeable battery with respect to a short term discharge
limiting voltage and a short term discharge suspension voltage of
when the upper limit lowering process by the monitoring section of
FIG. 2 is performed in time of engine start;
[0015] FIG. 5 is a flowchart showing an output control method of
the rechargeable battery performed by the battery ECU of FIG.
2;
[0016] FIG. 6 is a graph showing changes in the SOC of the
rechargeable battery when an upper limit lowering process value is
performed according to a second embodiment of the present
invention;
[0017] FIG. 7 is a graph showing changes in the SOC of the
rechargeable battery during a short term discharge suspension SOC
when the engine is being started in the second embodiment;
[0018] FIG. 8 is a flowchart showing an output controlling method
of the rechargeable battery in the second embodiment; and
[0019] FIG. 9 is a flowchart showing an output controlling method
of the rechargeable battery according to a third embodiment of the
present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0020] In the drawings, like numerals are used for like elements
throughout.
[0021] One aspect of the present invention is a controller for a
rechargeable battery mounted on a vehicle using an engine as a
power source. The vehicle includes a starter motor for starting the
engine and a vehicle controller for controlling the starter motor.
The controller includes a control unit that when operated instructs
the vehicle controller to stop discharging the rechargeable battery
when an index indicating a charged state of the rechargeable
battery satisfies a discharge suspension condition, and moderates
the discharge suspension condition when the rechargeable battery is
expected to supply power to the starter motor.
[0022] In the controller, the index indicating the charged state of
the rechargeable battery includes terminal voltage of the
rechargeable battery. The discharge suspension condition includes a
lower limit value for the terminal voltage of the rechargeable
battery. The control unit lowers the lower limit value of the
terminal voltage to moderate the discharge suspension
condition.
[0023] In the controller, the index indicating the charged state of
the rechargeable battery includes a state of charge of the
rechargeable battery. The discharge suspension condition includes a
lower limit value for the state of charge of the rechargeable
battery. The control unit lowers the lower limit value of the state
of charge to moderate the discharge suspension condition.
[0024] In the controller, the index indicating the charged state of
the rechargeable battery includes terminal voltage and state of
charge of the rechargeable battery. The discharge suspension
condition includes lower limit values for the terminal voltage and
state of charge of the rechargeable battery. The control unit
lowers the lower limit values of the terminal voltage and state of
charge of the rechargeable battery to moderate the discharge
suspension condition.
[0025] In the controller, the rechargeable battery has a
temperature, and the control unit moderates the discharge
suspension condition if the temperature of the rechargeable battery
is lower than or equal to a predetermined temperature when the
rechargeable battery is expected to supply power to the starter
motor.
[0026] In the controller, the control unit includes a monitor unit
for changing the discharge suspension condition so as to continue
discharging the rechargeable battery when the rechargeable battery
is expected to supply power to the starter motor.
[0027] In the controller, the control unit includes a setting unit
for setting a first upper limit value and a second upper limit
value, which is lower than the first upper limit value, for power
discharged from the rechargeable battery within a predetermined
time. The discharge suspension condition includes a first condition
for generating an instruction based on the first upper limit value
to stop discharging the rechargeable battery and a second condition
for generating an instruction based on the second upper limit value
to stop discharging the rechargeable battery. The control unit
moderates at least the first condition.
[0028] In the controller, the first upper limit value is set to be
higher than the power required to be discharged when starting the
engine.
[0029] In the controller, the control unit moderates the first
condition during a period in which an engine start signal provided
from the vehicle controller to the rechargeable battery controller
is active.
[0030] A further aspect of the present invention is a method for
controlling output of a rechargeable battery mounted on a vehicle
using an engine as a power source. The vehicle includes a starter
motor for starting the engine and a vehicle controller for
controlling the starter motor. The method includes determining
whether an index indicating a charged state of the rechargeable
battery satisfies a discharge suspension condition, instructing the
vehicle controller to stop discharging the rechargeable battery
when the index indicating the charged state of the rechargeable
battery satisfies the discharge suspension condition, determining
whether the rechargeable battery is expected to supply power to the
starter motor, and moderating the discharge suspension condition
when the rechargeable battery is expected to supply power to the
starter motor.
[0031] In the method, the index indicating the charged state of the
rechargeable battery includes terminal voltage of the rechargeable
battery, the discharge suspension condition includes a lower limit
value for the terminal voltage of the rechargeable battery, and
said moderating the discharge suspension condition includes
lowering the lower limit value of the terminal voltage.
[0032] In the method, the index indicating the charged state of the
rechargeable battery includes a state of charge of the rechargeable
battery, the discharge suspension condition includes a lower limit
value for the state of charge of the rechargeable battery, and said
moderating the discharge suspension condition includes lowering the
lower limit value of the state of charge.
[0033] In the method, the index indicating the charged state of the
rechargeable battery includes terminal voltage and state of charge
of the rechargeable battery, the discharge suspension condition
includes lower limit values for the terminal voltage and state of
charge of the rechargeable battery, and said moderating the
discharge suspension condition includes lowering the lower limit
values of the terminal voltage and state of charge of the
rechargeable battery.
[0034] The present invention may be a computer-readable product
encoded with a program for embodying the output controlling method
of the rechargeable battery. The output controlling method of the
rechargeable battery according to the present invention is
performed by installing the program in a computer and executing the
program.
[0035] The controller 1 for the rechargeable battery 40 and a
method for controlling the output of the rechargeable battery 40
according to a first embodiment of the present invention will now
be described with reference to FIGS. 1 to 5.
[0036] FIG. 1 is a schematic block diagram showing an electrical
configuration of a vehicle including a controller 1 for the
rechargeable battery 40.
[0037] As shown in FIG. 1, the vehicle including the controller 1
for the rechargeable battery 40 is an HEV. The vehicle includes an
internal combustion engine 24 and a motor 26, which function as a
power source for transmitting power to a drive shaft 28. The drive
shaft 28 is connected to vehicle wheels (not shown). When the
vehicle is motor-driven, the rechargeable battery 40 functions as a
power supply source for the motor 26.
[0038] The rechargeable battery 40 supplies power to the motor 26
via a relay unit 29 and an inverter 22. The rechargeable battery 40
also supplies power to a starter motor 38 for starting the engine
24 via the relay unit 29 and the inverter 22. The inverter 22
converts direct current from the rechargeable battery 40 to
alternating current for driving the motor 26. The wiring connecting
the inverter 22 and the starter motor 38 is not shown in FIG.
1.
[0039] The engine 24 transmits power to the vehicle wheels via a
power distribution mechanism 25, a decelerator 27, and a drive
shaft 28. The motor 26 transmits power to the vehicle wheels via
the decelerator 27 and the drive shaft 28. The power of the engine
24 is partially transmitted to an electric generator 23 via the
power distribution mechanism 25 when the rechargeable battery 40
requires charging.
[0040] The power generated by the electric generator 23 is supplied
to charge the rechargeable battery 40 via the inverter 22 and the
relay unit 29. The motor 26 is used as an electric generator when
the electric vehicle is decelerating or braking. The power
generated by the motor 26 is also supplied to charge the
rechargeable battery 40 via the inverter 22 and the relay unit
29.
[0041] The relay unit 29 includes relays 30 to 32, and a resistor
33. The relay 31 is connected between a positive terminal of the
rechargeable battery 40 and a high potential input terminal of the
inverter 22. The relay 32 is connected between a negative terminal
of the rechargeable battery 40 and the low potential input terminal
of the inverter 22. The relay 30 is connected in series with the
resistor 33 and in parallel with the relay 31. The relay 30 is used
with the resistor 33 to precharge a smoothing capacitor (not shown)
of the inverter 22 when activating the vehicle.
[0042] The electric motor vehicle includes a controller (battery
ECU) 1 for the rechargeable battery 40, a controller for the
vehicle (vehicle ECU) 20, and a controller for the engine (engine
ECU) 21. The engine ECU 21 mainly controls the ignition period and
the fuel injection amount of the engine 24. The battery ECU 1
mainly performs measurement of the terminal voltage, measurement of
the current, measurement of the temperature, calculation of SOC
(State Of Charge), deterioration determination of the rechargeable
battery 40, and transmits information on the results of each
process to the vehicle ECU 20. The specific configuration and
function of the battery ECU 1 will now be described with reference
to FIG. 2.
[0043] The vehicle ECU 20 controls the motor 26 and the starter
motor 38 by controlling the inverter 22 based on the information
provided from devices such as the battery ECU 1 and the engine ECU
21. The information provided from the engine ECU 21 includes the
operating state of the engine 24 and the rotational angle of the
crankshaft. The information provided from the battery ECU 1
includes information related to the SOC of the rechargeable battery
40 and the upper limit value of the discharging power of the
rechargeable battery 40. Information indicating the operation
amount of an accelerator pedal 37, the operation amount of a brake
pedal 36, and the gearshift range selected by a gearshift lever 35
are also provided to the vehicle ECU 20 and used to control the
inverter 22.
[0044] The vehicle ECU 20 supplies starting voltage (minimum
operation voltage) from the rechargeable battery 40 to the relays
30 to 32 to activate the relays 30 to 32. The vehicle ECU 20 also
suspends the supply of starting voltage to inactivate the relays 30
to 32. Specifically, the vehicle ECU 20 first activates the relay
30 and the relay 32 when the ignition (IG) 34 is switched to the
engine start position (IG-ON). This precharges the smoothing
capacitor of the inverter 22. Then, when the precharging is
terminated, the vehicle ECU 20 activates the relay 31.
Consequently, the power of the rechargeable battery 40 is supplied
to the motor 26 via the inverter 22. The vehicle ECU 20 suspends
the supply of the starting voltage when detecting that the ignition
34 has been switched to the OFF position.
[0045] When detecting that the ignition 34 has been switched to the
ON position, the vehicle ECU 20 transmits a signal indicating the
detection result to the battery ECU 1 before supplying the starting
voltage to the relays 30 to 32. When detecting that the ignition 34
has been switched to the OFF position, the vehicle ECU 20 transmits
a signal indicating the detection result to the battery ECU 1 and
simultaneously suspends the supply of the starting voltage.
[0046] Further, although not shown in the drawings, a relay for
activating and inactivating the starter motor 38 is arranged on the
wiring connecting the starter motor 38 and the inverter 22. After
detecting the IG-ON position and activating the relays 30 to 32,
the vehicle ECU 20 supplies the starting voltage from the
rechargeable battery 40 to the starter motor relay and activates
this relay. Power is then supplied to the starter motor 38, and the
engine is started by the driving force of the starter motor 38.
Furthermore, the vehicle ECU 20 provides the engine start signal to
the battery ECU 1 when detecting the IG-ON position.
[0047] In the first embodiment, the rechargeable battery 40
includes battery blocks B.sub.1, to B.sub.20 connected in series.
The battery blocks B.sub.1, to B.sub.20 are accommodated in a
battery case 42. Each battery block B.sub.1, to B.sub.20 is formed
by electrically connecting two battery modules in series.
Furthermore, each battery module is formed by electrically
connecting six battery cells 41 in series. Each battery cell 41 is
a nickel-metal hydride battery, a lithium ion battery, or the like.
The number of battery blocks, the number of battery modules, and
the number of battery cells 41 are not particularly limited. The
connection of the rechargeable battery 40 is also not limited to
the above example.
[0048] A plurality of temperature sensors 17 are arranged in the
battery case 42. The plurality of temperature sensors 43 are
arranged so that each temperature sensor 43 is associated with
either a battery block group of battery blocks having relatively
close temperatures or a battery block group of battery blocks
having relatively large temperature differences. The grouping of
the battery blocks is based on the temperatures of the battery
blocks measured in advance through experiments etc.
[0049] The configuration of the controller 1 for the rechargeable
battery 40 of the first embodiment will now be described with
reference to FIG. 2. FIG. 2 is a block diagram schematically
showing the configuration of the battery ECU 1 shown in FIG. 1. As
shown in FIG. 2, the battery ECU 1 includes a current measurement
unit 2, a voltage measurement unit 4, a temperature measurement
unit 3, a control unit 5, and a storage unit (memory) 6.
[0050] The voltage measurement unit 4 measures the terminal voltage
of the rechargeable battery 40. In the first embodiment, the
voltage measurement unit 4 measures terminal voltages (block
voltages) V.sub.u1 to V.sub.u20 of the respective battery blocks
B.sub.1 to B.sub.20. The voltage measurement unit 4 then generates
voltage data indicating each terminal voltage V.sub.u1 to V.sub.u20
and provides the voltage data to the control unit 5. The voltage
measurement unit 4 provides the voltage data to the control unit 5
in predetermined cycles. The control unit 5 stores the received
voltage data in the storage unit 6.
[0051] The current measurement unit 2 measures the current value I
of the charge current and the current value I of the discharge
current of the rechargeable battery 40. In the first embodiment,
the current measurement unit 2 converts the analog signal provided
from the current sensor 44 to a digital signal. The current
measurement unit 2 then generates current data indicating the
current value I of the current charged in the rechargeable battery
40 during charging and the current value I of the current
discharged from the rechargeable battery 40 during discharging
based on the digital signal and provides the current data to the
control unit 5. The current measurement unit 2 generates the
current data with the current value during charging as a negative
value and the current value during discharging as a positive value.
The current measurement unit 2 provides the current data to the
control unit 5 in predetermined cycles. The control unit 5 stores
the received current data in the storage unit 6.
[0052] The temperature measurement unit 3 measures the temperature
of the rechargeable battery 40. In the first embodiment, the
temperature measurement unit 3 receives an analog signal from the
temperature sensor 43, which are respectively associated with the
groups of battery blocks, and converts the analog signal to a
digital signal. The temperature measurement unit 3 then generates
temperature data indicating the battery temperature for each group
based on the digital signal and provides the temperature data to
the control unit 5. The temperature measurement unit 3 provides the
temperature data to the control unit 5 in predetermined cycles. The
control unit 5 stores the received temperature data in the storage
unit 6.
[0053] The control unit 5 includes a condition setting unit 7, a
monitor unit 8, a communication unit 9, and a calculation unit 10.
In the first embodiment, the condition setting unit 7 sets the
upper limit value of the discharging power that can be supplied
from the rechargeable battery 40 within a predetermined time.
Specifically, the condition setting unit 7 sets a short term output
upper limit (hereinafter referred to as first upper limit value) Pp
and a long term output upper limit (hereinafter referred to as
second upper limit value) Pn. The first upper limit value Pp and
the second upper limit value Pn set by the condition setting unit 7
are respectively stored in the storage unit 6 as short term output
information and long term output information.
[0054] The first upper limit value Pp indicates the upper limit
value of the discharging power that can be supplied from the
rechargeable battery 40 within a short predetermined time of, for
example, one to two seconds. The first upper limit value Pp is used
to limit the discharge of the rechargeable battery when the
rechargeable battery 40 is required to output a high discharge
within a short period of time such as when the vehicle starts to
move, when a gear is shifted, or when the engine is started. The
second upper limit value Pn indicates the upper limit of the
discharging power that can be supplied from the rechargeable
battery 40 in a relatively long period of time of, for example, ten
seconds. The second upper limit value Pn is used to limit the
discharge of the rechargeable battery when, for example, the
vehicle is traveling in a stable state.
[0055] In the first embodiment, the condition setting unit 7 sets
the first upper limit value Pp and the second upper limit value Pn
using a two-dimensional map of which the parameters are the battery
temperature and the SOC. Specifically, in the two-dimensional map,
the optimal upper limit value is recorded at an intersection of a
vertical axis (or horizontal axis) indicating the battery
temperature and the horizontal axis (or the vertical axis)
indicating the SOC. Each optimal value of the first upper limit
value Pp and the second upper limit value Pn recorded on the
two-dimensional map is obtained in advance through experiments. The
two-dimensional map is stored in the storage unit 6. The condition
setting unit 7 specifies the lowest battery temperature (minimum
battery temperature) in the battery temperatures of the battery
block groups based on the temperature data. The condition setting
unit 7 applies the minimum battery temperature and the SOC
estimated by the calculation unit 10 to the two-dimensional map to
set the optimal first upper limit value Pp and the second upper
limit value Pn.
[0056] Furthermore, in the first embodiment, the condition setting
unit 7 also sets a short term discharge limiting voltage
(hereinafter referred to as first limiting voltage) V.sub.1 and a
short term discharge suspension voltage (hereinafter referred to as
first suspension voltage) V.sub.2 (V.sub.1>V.sub.2) for the
first upper limit value Pp. The condition setting unit 7 also sets
a long term discharge limiting voltage (hereinafter referred to as
second limiting voltage) V.sub.11 and a long term discharge
suspension voltage (hereinafter referred to as second suspension
voltage) V.sub.12 (V.sub.11>V.sub.12) for the second upper limit
value Pn.
[0057] Each of the first limiting voltage V.sub.1 and the second
limiting voltage V.sub.11 is set as a trigger voltage when the
monitor unit 8 lowers the first upper limit value Pp and the second
upper limit value Pn. Each of the first suspension voltage V.sub.2
and the second suspension voltage V.sub.12 is set as a trigger
voltage when the monitor unit 8 suspends discharging.
[0058] The storage unit 6 stores a map showing the correlation
between the temperature and the first limiting voltage V.sub.1
optimal for that temperature and a map showing the correlation
between the temperature and the first suspension voltage V.sub.2
optimal for that temperature. Also, the storage unit 6 stores a map
showing the correlation between the temperature and the second
limiting voltage V.sub.11 optimal for that temperature and a map
showing the correlation between the temperature and the second
suspension voltage V.sub.12 optimal for that temperature. The
condition setting unit 7 sets the first limiting voltage V.sub.1,
the first suspension voltage V.sub.2, the second limiting voltage
V.sub.11, and the second suspension voltage V.sub.12 by applying
the minimum battery temperature to each map.
[0059] Each map is generated taking into account the performance
and load of the rechargeable battery 40 based on results of
discharging experiments performed in advance. In particular, the
map specifying the first suspension voltage V.sub.2 and the map
specifying the second suspension voltage V.sub.12 are generated so
as to avoid the occurrence of polarity inversion in the battery
cells 41 of the rechargeable battery 40.
[0060] The monitor unit 8 lowers the upper limit value to suppress
a decrease in the terminal voltage of the rechargeable battery 40
when the terminal voltage of the rechargeable battery 40 decreases
to the discharge limiting voltage. The monitor unit 8 also stops
the discharge when the terminal voltage of the rechargeable battery
40 further decreases and reaches the discharge suspension
voltage.
[0061] FIG. 3 is a graph showing changes in the terminal voltage of
the rechargeable battery 40 when the upper limit value is lowered
by the monitor unit 8 of FIG. 2.
[0062] First, the monitor unit 8 specifies the lowest terminal
voltage (minimum terminal voltage) Vu_min in the terminal voltages
V.sub.u1 to V.sub.u20 measured for the battery blocks. As shown at
time T.sub.1 of FIG. 3, when Vu_min decreases to the second
limiting voltage V.sub.11, the monitor unit 8 resets the second
upper limit value Pn to a value that is one step smaller and lowers
the second upper limit value Pn. The monitor unit 8 also rewrites
the long term output information to information corresponding with
the second upper limit value Pn.
[0063] Next, as shown at time T.sub.2 of FIG. 3, when Vu_min
decreases to the first limiting voltage V.sub.1, the monitor unit 8
resets the first upper limit Pp to a value one step smaller and
lowers the first upper limit value Pp. The monitor unit 8 also
rewrites the short term output information to information
corresponding to the first upper limit value Pp. The lowering width
of each of the second upper limit value Pn and the first upper
limit value Pp is set in accordance with the performance of the
rechargeable battery 40 and the lowering speed of the voltage and
is not particularly limited.
[0064] As shown at time T.sub.3 of FIG. 3, when Vu_min decreases to
the second suspension voltage V.sub.12, the monitor unit 8
determines to suspend the discharge for the long term, resets the
second upper limit value Pn to zero (0) and rewrites the long term
output information. Furthermore, as shown at time T.sub.4 of FIG.
3, when Vu_min decreases to the first suspension voltage V.sub.2,
the monitor unit 8 determines to suspend the discharge for the
short term, resets the first upper limit value Pp to zero (0), and
rewrites the short term output information.
[0065] In this manner, the monitor unit 8 lowers the first upper
limit value Pp and the second upper limit value Pn in accordance
with the decrease in the terminal voltage of the rechargeable
battery 40 to suppress the lowering of the terminal voltage. The
monitor unit 8 also suspends the discharge when the terminal
voltage of the rechargeable battery 40 further decreases to a
predetermined suspension voltage to suppress deterioration of the
rechargeable battery. The monitor unit 8 performs the above
processes constantly or in regular intervals.
[0066] However, if the monitor unit 8 performs the process shown in
FIG. 3 in the same manner as under normal temperatures even though
the terminal voltage of the rechargeable battery decreases under
low temperatures such as zero degrees Celsius or lower, power would
not be supplied to the starter motor 38, and the engine 24 may not
be started. Thus, in the first embodiment, the monitor unit 8
lowers the respective values of the first limiting voltage V.sub.1
and the first suspension voltage V.sub.2 particularly when starting
the engine. This will be described with reference to FIG. 4. In the
first embodiment, the first limiting voltage V.sub.1 after being
lowering is referred to as "the short term discharge limiting
voltage V.alpha. (first limiting voltage V.alpha.)" and the first
suspension voltage V.sub.2 after being lowered is referred to as
"the short term discharge suspension voltage V.beta. (first
suspension voltage V.beta.)".
[0067] FIG. 4 is a graph showing changes in the terminal voltage of
the rechargeable battery 40 with respect to the first limiting
voltage and the first suspension voltage of when the upper limit
value is lowered by the monitor unit 8 of FIG. 2 during the
starting of the engine. As shown in FIG. 4, the monitor unit 8
lowers the first limiting voltage from V.sub.1 to V.alpha. and
lowers the first suspension voltage from V.sub.2 to V.beta. when
the supply of power to the starter motor 38 (see FIG. 1) by the
rechargeable battery 40 is expected, specifically, when the engine
start signal is provided from the vehicle ECU 20 to the battery ECU
1. The monitor unit 8 preferably lowers the first limiting voltage
and the first suspension voltage to V.alpha. and V.beta.,
respectively, in the period from time T.sub.1 to T.sub.5 shown in
FIG. 4 when the logic level of the engine start signal is switched
from low to high.
[0068] Therefore, as shown in FIG. 4, the first upper limit value
Pp cannot be lowered (see T.sub.2) even if the minimum terminal
voltage Vu_min decreases to the first limiting voltage V.sub.1.
When Vu_min decreases to the first limiting voltage V.alpha., the
first upper limit value Pp is lowered for the first time (see
T.sub.3) The discharge is not suspended even if Vu_min is decreased
to the first suspension voltage V.sub.2 by the supply of power to
the starter motor 38. That is, the discharge is not suspended
unless Vu_min decreases to the first suspension voltage V.beta..
Therefore, the supply of power to the starter motor 38 is
continued.
[0069] As a result, the reliability of the starting of the engine
is improved even under low temperatures. The lowering width of the
first limiting voltage V.sub.1 and the first suspension voltage
V.sub.2 is appropriately set so as to avoid the occurrence of
polarity inversion in each battery cell 41 of the rechargeable
battery 40, while taking into account the performance of the
rechargeable battery 40.
[0070] The communication unit 9 transmits the first upper limit
value Pp and the second upper limit value Pn to the vehicle ECU 20
mounted on the vehicle. In the first embodiment, the communication
unit 9 transmits the short term output information (information
corresponding to the first upper limit value Pp) and the long term
output information (information corresponding to the second upper
limit value Pp) stored in the storage unit 6 to the vehicle ECU 20.
The short term output information and the long term output
information are transmitted to the vehicle ECU 20 in regular time
intervals or whenever the monitor unit 8 performs a lowering or
raising process.
[0071] When the short term output information and the long term
output information are provided to the vehicle ECU 20, the use of
the rechargeable battery 40 by the vehicle ECU 20 is restricted to
the first upper limit value Pp and the second upper limit value Pn.
That is, the vehicle ECU 20 uses the rechargeable battery 40 within
the range of the first upper limit value Pp specified by the short
term output information or within the range of the second upper
limit value Pn specified by the long term output information to
control the driving of the motor 26 (see FIG. 1) and the starter
motor 38 (see FIG. 1).
[0072] The calculation unit 10 estimates the SOC of the
rechargeable battery 40. The estimated SOC is transmitted to the
vehicle ECU 20 by the communication unit 9. In the first
embodiment, the calculation unit 10 estimates the first SOC based
on the accumulated capacitance Q of the rechargeable battery 40.
The calculation unit 10 also estimates the second SOC based on the
charge and discharge history. Furthermore, the calculation unit 10
obtains the difference between the first SOC and the second SOC,
corrects the first SOC based on the obtained difference, and
acquires the corrected first SOC as the SOC of the rechargeable
battery 40.
[0073] Specifically, the estimation of the first SOC is performed
through the following procedures. First, the calculation unit 10
reads the current data stored in the storage unit 6, acquires the
current value I, and multiplies the current value I with the
charging efficiency when the acquired current value I is negative
during charging. The calculation unit 10 then accumulates the
obtained current value I (multiplied value during charging) over a
predetermined time to calculate the accumulated capacitance Q. The
calculation unit 10 further obtains the difference between the
capacitance in a state of full charge, which is obtained in advance
through experiments, and the accumulated capacitance Q. The
calculation unit 10 then obtains the ratio of the obtained
difference with respect to the capacitance in a state of full
charge and estimates the obtained ratio [%] as the first SOC.
[0074] The estimation of the second SOC is performed through the
following procedures. First, the calculation unit 10 acquires two
pieces of data, the voltage value of the terminal voltage and
either the current value I of the charge current or the discharge
current for each battery block, from the voltage data provided from
the voltage measurement unit 4 and the current data provided from
the current measurement unit 2 within a predetermined period of
time. The two acquired pieces of data are stored in the storage
unit 6 as charge and discharge history.
[0075] The calculation unit 10 then selects the average pair data
excluding the upper limit and the lower limit of the representative
battery block from the two pieces of data for each block stored in
the storage unit 6. Furthermore, the calculation unit 10 obtains a
primary approximation line (V-I approximation line) by performing a
regression analysis on the two pieces of selected data. The
calculation unit 10 then acquires the V segment of the V-I
approximation line as a non-load voltage OCV of a representative
battery block.
[0076] The calculation unit 10 estimates the polarization voltage
of the rechargeable battery 40 based on the amount of change
.DELTA.Q per predetermined period (or unit time) of the accumulated
capacitance Q. Specifically, the calculation unit 10 performs a
time delay process and an averaging process on the amount of change
.DELTA.Q to eliminate variation components corresponding to
unnecessary high frequency components of .DELTA.Q and calculates
.DELTA.Q'. The calculation unit 10 applies the calculated amount of
change .DELTA.Q' and the minimum battery temperature to the
two-dimensional map that represents the polarization voltage at the
intersection of the vertical axis (or horizontal axis) indicating
the temperature and the horizontal axis (or the vertical axis)
indicating .DELTA.Q' to specify the polarization voltage. The
calculation unit 10 estimates the specified polarization voltage as
the polarization voltage of the rechargeable battery 40. This
two-dimensional map is also stored in the storage unit 6.
[0077] The calculation unit 10 subtracts the estimated polarization
voltage from the non-load voltage OCV of the representative battery
block to calculate the electromotive force of the representative
battery block. The calculation unit 10 also applies the calculated
electromotive force and the minimum battery temperature to the
two-dimensional map that represents the SOC at the intersection of
the vertical axis (or the horizontal axis) indicating the
temperature and the horizontal axis (or the vertical axis)
indicating the electromotive force to specify the SOC and estimates
such SOC as the second SOC. This two-dimensional map is also stored
in the storage unit 6.
[0078] In the above example, the calculation unit 10 selects a
representative battery block and calculates the OCV but is not
limited in such a manner. For example, the calculation unit 10 may
calculate the electromotive force of the entire rechargeable
battery from the non-load voltage of the entire rechargeable
battery to estimate the second SOC.
[0079] The output controlling method of the rechargeable battery 40
of the first embodiment will now be described with reference to
FIG. 5. FIG. 5 is a flowchart showing the output controlling method
of the rechargeable battery 40 of the first embodiment. The output
controlling method of the rechargeable battery 40 of the first
embodiment is performed by operating the battery ECU (battery
controller) 1 shown in FIGS. 1 and 2.
[0080] As shown in FIG. 5, the condition setting unit 7 first sets
the short term output upper limit value (first upper limit value)
Pp, the short term discharge limiting voltage (first limiting
voltage) V.sub.1, and the short term discharge suspension voltage
(first suspension voltage) V.sub.2 (step S1) The condition setting
unit 7 then sets the long term output upper limit value (second
upper limit value) Pn, the long term discharge limiting voltage
(second limiting voltage) V.sub.11, and the long term discharge
suspension voltage (second suspension voltage) V.sub.12 (step S2).
The steps S1 and S2 may be performed simultaneously or in a
reversed order.
[0081] The monitor unit 8 determines whether or not the engine
start signal is output from the vehicle ECU 20 (step 3). If the
engine start signal is output, the monitor unit 8 lowers the first
limiting voltage V.sub.1 to the first limiting voltage V.alpha. and
lowers the first suspension voltage V.sub.2 to the second
suspension voltage V.beta. (step S4). Then, the monitor unit 8
proceeds to step 5. If the engine start signal is not output, the
monitor unit 8 performs step S5 without lowering the first limiting
voltage V.sub.1 or the first suspension voltage V.sub.2.
[0082] In step S5, the monitor unit 8 determines whether or nor the
minimum terminal voltage Vu_min is less than or equal to the second
limiting voltage V.sub.11. If the minimum terminal voltage Vu_min
is not less than or equal to the second limiting voltage V.sub.11,
the monitor unit 8 proceeds to step S9. If the minimum terminal
voltage Vu_min is less than or equal to the second limiting voltage
V.sub.11, the monitor unit 8 determines whether or not the minimum
terminal voltage Vu_min is less than or equal to the second
suspension voltage V.sub.12 (step S6).
[0083] If determined in step S6 that the minimum terminal voltage
Vu_min is less than or equal to the second suspension voltage
V.sub.12, the monitor unit 8 sets the second upper limit value Pn
to 0 (zero) to suspend the discharge for a long term (step S8) and
then proceeds to step S9. If determined in step S6 that the minimum
terminal voltage Vu_min is not less than or equal to the second
suspension voltage V.sub.12, the monitor unit 8 lowers the second
upper limit value Pn by one step (step S7) and then proceeds to
step S9.
[0084] In step S9, the monitor unit 8 determines whether or not the
minimum terminal voltage Vu_min is less than or equal to the first
limiting voltage V.sub.1. However, if step S4 is performed, the
monitor unit 8 determines whether or not the minimum terminal
voltage Vu_min is less than or equal to the first limiting voltage
V.alpha. in step S9.
[0085] When the minimum terminal voltage Vu_min is not less than or
equal to the first limiting voltage V.sub.1 (or V.alpha.), the
monitor unit 8 performs step S13. When the minimum terminal voltage
Vu_min is less than or equal to the first limiting voltage V1 (or
V.alpha.), the monitor unit 8 determines whether or not the minimum
terminal voltage Vu_min is less than or equal to the first
suspension voltage V2 (step S10). However, the monitor unit 8
determines whether or not the minimum terminal voltage Vu_min is
less than or equal to the first suspension voltage V.beta. in step
S10 if step S4 is performed.
[0086] If determined in step S10 that the minimum terminal voltage
Vu_min is less than or equal to the first suspension voltage
V.sub.2 (or V.beta.), the monitor unit 8 sets the first upper limit
value Pp to 0 (zero) to suspend discharge for the short term (step
S12). If determined in step S10 that the minimum terminal voltage
Vu_min is not less than or equal to the first suspension voltage
V.sub.2 (or V.beta.), the monitor unit 8 lowers the first upper
limit value Pp by one step (step S11).
[0087] Subsequently, the communication unit 9 provides the short
term output information and the long term output information to the
vehicle ECU 20 (step S13) and then terminates processing. In the
first embodiment, the processes from steps S1 to S13 shown in FIG.
5 are performed in constant cycles (e.g., 100 ms cycles).
[0088] Therefore, according to the first embodiment, the first
limiting voltage V.sub.1 and the first suspension voltage V.sub.2
are lowered to V.alpha. and V.beta., respectively, when the engine
is started, and the discharge limiting condition and the discharge
suspension condition are moderated compared to normal states. As a
result, the first upper limit value Pp is lowered only when an
index (block voltage of the rechargeable battery 40) indicating the
charged state of the rechargeable battery 40 satisfies the
discharge suspension condition (lower limit value: V.beta.), which
is lower than that for normal states. Thus, this improves the
reliability of the starting of the engine under low temperatures.
Since the power necessary for engine start is ensured by lowering
the first suspension voltage, the engine is started without having
to repeatedly activate and inactivate the starter motor 38. Thus,
the deterioration of the rechargeable battery 40 is suppressed
compared to the prior art.
[0089] Although not shown in FIG. 5, the monitor unit 8 may also
determine whether or not the battery temperature of the
rechargeable battery 40 is lower than or equal to a constant value
(e.g. zero degrees) in step S3 of the first embodiment. In this
case, step S4 is performed only under low temperatures. Thus,
deterioration of the rechargeable battery 40 is further
suppressed.
[0090] In the first embodiment, the programs embodying various
processes shown in FIG. 5 may be installed in a microcomputer, and
the battery ECU 1 may execute the programs installed in the
microcomputer. In this case, a CPU (central processing unit) of the
microcomputer functions as the control unit 5. The connecting
circuit of the voltage sensor and the CPU function as the voltage
measurement unit 4, the connecting circuit of the current sensor 44
and the CPU function as the current measurement unit 2, and the
connecting circuit of the temperature sensor 43 and the CPU
function as the temperature measurement unit 3. Furthermore,
various memories arranged in the microcomputer function as the
storage unit 6.
[0091] In the field of HEV, the vehicle ECU may function as the
battery ECU. In this case, the programs embodying various processes
shown in FIG. 5 are installed in the microcomputer configuring the
vehicle ECU 20 and executed by the battery ECU 1.
[0092] A second embodiment of the present invention will now be
described with reference to FIGS. 6 to 8.
[0093] The rechargeable battery subject to control in the second
embodiment is similar to the rechargeable battery 40 of the first
embodiment shown in FIGS. 1 and 2. The controller for the
rechargeable battery of the second embodiment, which is similar to
the controller 1 for the rechargeable battery 40 of the first
embodiment shown in FIGS. 1 and 2, is mounted on the HEV. To avoid
redundancy, like or same reference numerals are given to those
components that are the same as the corresponding components of the
first embodiment.
[0094] FIG. 6 is a graph showing changes in the SOC of the
rechargeable battery 40 when the upper limit value is lowered by
the monitor unit 8 of the second embodiment. FIG. 7 is a graph
showing changes in the SOC of the rechargeable battery 40 with
respect to the short term discharge stop SOC when the upper limit
value is lowered by the monitor unit 8 of the second embodiment in
time of engine start.
[0095] As shown in FIGS. 6 and 7, the SOC of the rechargeable
battery 40 is used as an index indicating the charged state of the
rechargeable battery 40. Discharging is suspended when the SOC of
the rechargeable battery 40 decreases to a predetermined value.
[0096] Specifically, in the second embodiment, the condition
setting unit 7 sets the short term discharge suspension SOC
(hereinafter referred to as first suspension SOC) and the long term
discharge suspension SOC (hereinafter referred to as second
suspension SOC) instead of the short term discharge suspension
voltage (first suspension voltage) and the long term discharge
suspension voltage (second suspension voltage) of the first
embodiment as the trigger for stopping the discharge. The storage
unit 6 stores a map showing the correlation between the temperature
and the first suspension SOC optimal for that temperature and a map
showing the correlation between the temperature and the second
suspension SOC optimal for that temperature. The condition setting
unit 7 applies the minimum battery temperature specified from the
temperature data to each map to set the first suspension SOC and
the second suspension SOC.
[0097] Thus, as shown in FIG. 6, the monitor unit 8 determines to
suspend discharge in the long term when the value of the SOC of the
rechargeable battery 40 decreases to value B of the second
suspension SOC and resets (see T.sub.1) the second upper limit
value Pn to 0 (zero). The monitor unit 8 further determines to
suspend discharge in the short term when the value of the SOC of
the rechargeable battery 40 decreases to the value A of the first
suspension SOC and resets (see T.sub.2) the first upper limit value
Pp to 0 (zero).
[0098] However, it becomes difficult to start the engine when the
SOC of the rechargeable battery 40 decreases under low
temperatures. Thus, the monitor unit 8 lowers the value of the
first suspension SOC particularly when starting the engine in the
second embodiment.
[0099] For example, as shown in FIG. 7, the monitor unit 8 lowers
the value of the first suspension SOC from A to a (A>a) when the
logic level of the engine start signal switches from low to high.
As a result, the discharge is not suspended even if the value of
the SOC of the rechargeable battery 40 decreases to A by the power
supply to the starter motor 38, as shown in FIG. 7. That is,
discharge is not suspended unless the value of the SOC decreases to
a. Therefore, the supply of power to the starter motor 38 is
continued.
[0100] Consequently, the reliability of the starting of the engine
is improved even under low temperatures. The lowering width of the
first suspension SOC is set so as to avoid the occurrence of
polarity inversion in the battery cells of the rechargeable battery
40 taking into account the performance of the rechargeable battery
40.
[0101] The output controlling method of the rechargeable battery 40
of the second embodiment will now be described with reference to
FIG. 8. FIG. 8 is a flowchart showing the output controlling method
of the rechargeable battery 40 of the second embodiment. The output
controlling method of the rechargeable battery 40 in the second
embodiment is performed by operating the battery ECU 1 (battery
controller) of the second embodiment.
[0102] As shown in FIG. 8, the condition setting unit 7 first sets
the short term output upper limit value (first upper limit value)
Pp, the short term discharge limiting voltage (first limiting
voltage ) V.sub.1, and the short term discharge suspension SOC
(first suspension SOC) (step S21). The condition setting unit 7
also sets the long term output upper limit value (second upper
limit value) Pn, the long term discharge limiting voltage (second
limiting voltage) V.sub.11, and the long term discharge suspension
SOC (first suspension SOC) (step S22). Steps S21 and S22 may be
performed simultaneously or in a reversed order. The value of the
first suspension SOC is set to A in step S21, and the value of the
second suspension SOC is set to B in step S22.
[0103] The monitor unit 8 determines whether or not the engine
start signal is output from the vehicle ECU 20 (step S23). Step S23
is similar to step S3 of the first embodiment shown in FIG. 5.
[0104] When the engine start signal is output, the monitor unit 8
lowers the value of the first suspension SOC from A to a (step S24)
and then proceeds to step S25. In step S24, the monitor unit 8
lowers the value of the first limiting value V.sub.1 in the same
manner as in step S4 of the first embodiment. When the engine start
signal is not output, the monitor unit 8 performs step S25 without
lowering the first suspension SOC. The lowered first limiting
voltage is set as the "first limiting voltage V.alpha.".
[0105] In step S25, the monitor unit 8 determines whether or not
the minimum terminal voltage Vu_min is less than or equal to the
second limiting voltage V.sub.11. If the minimum terminal voltage
Vu_min is not less than or equal to the second limiting voltage
V.sub.11, the monitor unit 8 performs step S29. If the minimum
terminal voltage Vu_min is less than or equal to the second
limiting voltage V.sub.11, the monitor unit 8 determines whether or
not the value of the SOC of the rechargeable battery 40 is less
than or equal to the value B of the second suspension SOC (step
S26).
[0106] If determined in step S26 that the value of the SOC of the
rechargeable battery 40 is less than or equal to the value B of the
second suspension SOC, the monitor unit 8 sets the second upper
limit value Pn to 0 (zero) to suspend the discharge for the long
term (step S28) and then proceeds to step 29. If determined in step
S26 that the value of the SOC of the rechargeable battery 40 is not
less than or equal to the value B of the second suspension SOC, the
monitor unit 8 lowers the second upper limit value Pn by one step
(step S27) and then proceeds to step S29.
[0107] In step S29, the monitor unit 8 determines whether or not
the minimum terminal voltage Vu_min is less than or equal to the
first limiting voltage V.sub.1. If step S24 is performed, the
monitor unit 8 determines whether or not the minimum terminal
voltage Vu_min is less than or equal to the first limiting voltage
V.alpha. in step S29. Step S29 is similar to step S9 of the first
embodiment shown in FIG. 5.
[0108] If the minimum terminal voltage Vu_min is not less than or
equal to the first limiting voltage V.sub.1 (or V.alpha.), the
monitor unit 8 performs step S33. If the minimum terminal voltage
Vu_min is less than or equal to the first limiting voltage V.sub.1
(or V.alpha.), the monitor unit 8 determines whether or not the
value of the SOC of the rechargeable battery 40 estimated by the
calculation unit 10 is less than or equal to the value A of the
first suspension SOC (step S30). If step S24 is performed, the
monitor unit 8 determines whether or not the value of the SOC of
the rechargeable battery 40 is less than or equal to the value a of
the first suspension SOC in step S30.
[0109] If determined in step S30 that the value of the SOC of the
rechargeable battery 40 is less than or equal to the value A (or a)
of the second suspension SOC, the monitor unit 8 sets the first
upper limit value Pp to 0 (zero) to suspend the discharge for the
short term (step S32). If determined in step S30 that the value of
the SOC of the rechargeable battery 40 is not less than or equal to
the value A (or a) of the first suspension SOC, the monitor unit 8
lowers the first upper limit value Pp by one step (step S31).
[0110] Subsequently, the communication unit 9 provides the short
term output information and the long term output information to the
vehicle ECU 20 (step S33) and terminates the processing. Step S33
is similar to step S13 of the first embodiment shown in FIG. 5. The
processes of steps S21 to S33 shown in FIG. 8 are also performed at
a constant cycle (e.g., 100 ms cycle) in the second embodiment.
[0111] In this manner, in the second embodiment, the value of the
first suspension SOC is lowered from A to a when the engine is
started, and the discharge suspension condition is moderated
compared to normal states. As a result, the first upper limit value
Pp is lowered only when the index (SOC of rechargeable battery 40)
indicating the charged state of the rechargeable battery 40
satisfies the discharge suspension condition (lower limit value: a
herein) which is more moderate than that for normal states.
Therefore, the reliability for starting the engine under lower
temperatures is enhanced in the second embodiment in the same
manner as in the first embodiment. Since the power necessary for
starting the engine is ensured by lowering the first suspension
SOC, the engine is started without repeatedly activating and
inactivating the starter motor 38. Thus, the deterioration of the
rechargeable battery 40 is also suppressed in the second embodiment
compared to the prior art in the same manner as in the first
embodiment.
[0112] Although not shown in FIG. 8, the monitor unit 8 may
determine whether or not the battery temperature of the
rechargeable battery 40 is lower than or equal to a constant value
(e.g. zero degrees) in step S23 of the second embodiment. In this
case, step S24 is performed only under low temperatures. Thus,
deterioration of the rechargeable battery 40 is further
suppressed.
[0113] In the second embodiment, the programs embodying various
processes shown in FIG. 8 are installed in the microcomputer, and
the battery ECU 1 executes the programs installed in the
microcomputer.
[0114] A third embodiment of the present invention will now be
described with reference to FIG. 9.
[0115] The rechargeable battery subject to control in the third
embodiment has the same configuration as the rechargeable battery
40 of the first embodiment shown in FIGS. 1 and 2. The controller
for the rechargeable battery of the third embodiment, which is
similar to the controller 1 for the rechargeable battery 40 of the
first embodiment shown in FIGS. 1 and 2, is mounted on an HEV. To
avoid redundancy, like or same reference numerals are given to
those components that are the same as the corresponding components
of the first embodiment.
[0116] In the third embodiment, the terminal voltage (block
voltage) of the rechargeable battery 40 and the SOC of the
rechargeable battery 40 are both used as indexes indicating the
charged state of the rechargeable battery 40. The discharge is
suspended when the terminal voltage and the SOC of the rechargeable
battery 40 are both lowered to a predetermined value.
[0117] Specifically, in the third embodiment, the condition setting
unit 7 sets the short term discharge suspension SOC (first
suspension SOC) and the long term discharge suspension SOC (second
suspension SOC) in addition to the short term discharge suspension
voltage (first suspension voltage) V.sub.2 and the long term
discharge suspension voltage (second suspension voltage) V.sub.12
as the trigger for suspending the discharge. The setting of the
first suspension voltage V.sub.2 and the second suspension voltage
V.sub.12 with the condition setting unit 7 is performed in the same
manner as in the first embodiment. The setting of the first
suspension SOC and the second suspension SOC by the condition
setting unit 7 is performed in the same manner as in the second
embodiment.
[0118] In the third embodiment, the monitor unit 8 lowers the first
limiting voltage V.sub.1, the first suspension voltage V.sub.2 and
the value of the first suspension SOC to enhance the reliability of
the starting of the engine start under conditions in which it is
difficult to start the engine, such as under low temperatures.
[0119] The output controlling method of the rechargeable battery 40
of the third embodiment will now be described with reference to
FIG. 9. FIG. 9 is a flowchart showing the output controlling method
of the rechargeable battery 40 of the third embodiment. The output
controlling method of the rechargeable battery 40 in the third
embodiment is performed by operating the battery ECU 1 (battery
controller) of the third embodiment.
[0120] As shown in FIG. 9, the condition setting unit 7 first sets
the short term output upper limit value (first upper limit value)
Pp, the short term discharge limiting voltage (first limiting
voltage) V.sub.1, the short term discharge suspension voltage
(first suspension voltage) V.sub.2, and the short term discharge
suspension SOC (first suspension SOC) (step S41). The condition
setting unit 7 also sets the long term output upper limit value
(second upper limit value) Pn, the long term discharge limiting
voltage (second limiting voltage) V.sub.11, the long term discharge
suspension voltage (second suspension voltage) V.sub.12, and the
long term discharge suspension SOC (second suspension SOC) (step
S42). Steps S41 and S42 may be performed simultaneously or in a
reversed order. Furthermore, the value of the first suspension SOC
is set to A in step S41, and the value of the second suspension SOC
is set to B in step S42.
[0121] The monitor unit 8 then determines whether or not the engine
start signal is output from the vehicle ECU 20 (step S43). Step S43
is similar to step S3 of the first embodiment shown in FIG. 5.
[0122] If the engine start signal is output, the monitor unit 8
lowers the first limiting voltage V.sub.1 and the first suspension
voltage V.sub.2, and further lowers the value of the first
suspension SOC from A to a (step S44). The monitor unit 8
thereafter performs step S45. If the engine start signal is not
output, the monitor unit 8 performs step S45 without lowering the
first limiting voltage V.sub.1, the first suspension voltage
V.sub.2, and the first suspension SOC. The lowered first limiting
voltage is set as the "first limiting voltage V.alpha.", and the
lowered first suspension voltage is set as the "first suspension
voltage V.beta.".
[0123] In step S45, the monitor unit 8 determines whether or not
the minimum terminal voltage Vu_min is less than or equal to the
second limiting voltage V.sub.11. If the minimum terminal voltage
Vu_min is not less than or equal to the second limiting voltage
V.sub.11, the monitor unit 8 performs step S49. If the minimum
terminal voltage Vu_min is less than or equal to the second
limiting voltage V.sub.11, the monitor unit 8 determines whether or
not the minimum terminal voltage Vu_min is less than or equal to
the second suspension voltage V.sub.12, and whether or not the
value of the SOC of the rechargeable battery 40 is less than or
equal to the value B of the second suspension SOC (step S46).
[0124] If it is determined in step S46 that the minimum terminal
voltage Vu_min is less than or equal to the second suspension
voltage V.sub.12 and the value of the SOC of the rechargeable
battery 40 is less than or equal to the value B of the second
suspension SOC, the monitor unit 8 sets the second upper limit
value Pn to 0 (zero) to suspend the discharge for a long term (step
S48). The monitor unit 8 then performs step S49.
[0125] If it is determined in step S46 that the minimum terminal
voltage Vu_min is not less than or equal to the second suspension
voltage V.sub.12 and the value of the SOC of the rechargeable
battery 40 is not less than or equal to the value B of the second
suspension SOC, the monitor unit 8 lowers the second upper limit
value Pn by one step (step S47). The monitor unit 8 then performs
step S49.
[0126] In step S49, the monitor unit 8 determines whether or not
the minimum terminal voltage Vu_min is less than or equal to the
first limiting voltage V.sub.1. If step S44 is performed, the
monitor unit 8 determines whether or not the minimum terminal
voltage Vu_min is less than or equal to the first limiting voltage
V.alpha. in step S49. Step S49 is similar to step S9 of the first
embodiment shown in FIG. 5.
[0127] If the minimum terminal voltage Vu_min is not less than or
equal to the first limiting voltage V.sub.1 (or V.alpha.), the
monitor unit 8 performs step S53. If the minimum terminal voltage
Vu_min is less than or equal to the first limiting voltage V.sub.1
(or V.alpha.), the monitor unit 8 determines whether or not the
minimum terminal voltage Vu_min is less than or equal to the first
suspension voltage V.sub.2 and whether or not the value of the SOC
of the rechargeable battery 40 is less than or equal to the value A
of the first suspension SOC (step S50). If step S44 is performed,
the monitor unit 8 determines whether or not the minimum terminal
voltage Vu_min is less than or equal to the first suspension
voltage V.beta. and whether or not the value of the SOC of the
rechargeable battery 40 is less than or equal to the value a of the
first suspension SOC in step S50.
[0128] If determined in step S50 that the minimum terminal voltage
Vu_min is less than or equal to the first suspension voltage
V.sub.2 (or V.beta.) and the value of the SOC of the rechargeable
battery 40 is less than or equal to the value A (or a) of the first
suspension SOC, the monitor unit 8 sets the first upper limit value
Pp to 0 (zero) (step S52).
[0129] If determined in step S50 that the minimum terminal voltage
Vu_min is not less than or equal to the first suspension voltage
V.sub.2 (or V.beta.) and the value of the SOC of the rechargeable
battery 40 is not less than or equal to the value A (or a) of the
first suspension SOC, the monitor unit 8 lowers the first upper
limit value Pp by one step (step S51).
[0130] Subsequently, the communication unit 9 provides the short
term output information and the long term output information to the
vehicle ECU 20 (step S53) and ends the processing. Step S53 is
similar to step S13 of the first embodiment shown in FIG. 5. The
processes steps S41 to S53 shown in FIG. 9 are also performed in
constant cycles (e.g., 100 ms cycles) in the third embodiment.
[0131] In this manner, the discharge suspension condition (lower
limit value) is moderated when the engine is started in the third
embodiment. The reliability for starting the engine under low
temperatures is enhanced in the same manner as the first and second
embodiments. Furthermore, since the power necessary for starting
the engine is also ensured in the third embodiment, the engine is
started without repeatedly activating and inactivating the starter
motor 38. The deterioration of the rechargeable battery 40 is also
more suppressed compared to the prior art in the same manner as the
first and second embodiments.
[0132] Although not shown in FIG. 9, the monitor unit 8 may
determine whether or not the battery temperature of the
rechargeable battery 40 is lower than or equal to a constant value
(e.g., zero degree) in step S43 of the third embodiment. In this
case, step S44 is performed only under low temperatures. Thus,
deterioration of the rechargeable battery 40 is further
suppressed.
[0133] In the third embodiment as well, the programs embodying
various processes shown in FIG. 9 are installed in the
microcomputer, and the battery ECU 1 executes the programs
installed in the microcomputer.
[0134] The rechargeable battery subject to control in the present
invention is not limited to the rechargeable battery 40 for
supplying power to the motor used to move the vehicle as in the
first to the third embodiments. The rechargeable battery subject to
control in the present invention includes any kind of rechargeable
battery mounted on a vehicle to supply power to the starter
motor.
[0135] The device and method for controlling the output of a
rechargeable battery in the present invention are effective for a
rechargeable battery that supplies power to the starter motor of
the vehicle. That is, the present invention is not limited to an
HEV and is also effective for a typical engine automobile. The
device and method for controlling the output of a rechargeable
battery in the present invention have industrial applicability.
[0136] It should be apparent to those skilled in the art that the
present invention may be embodied in many other specific forms
without departing from the spirit or scope of the invention.
Therefore, the present examples and embodiments are to be
considered as illustrative and not restrictive, and the invention
is not to be limited to the details given herein, but may be
modified within the scope and equivalence of the appended
claims.
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